Cyclopropenium-activated Beckmann rearrangement. Catalysis versus self-propagation in reported organocatalytic Beckmann rearrangementsElectronic supplementary information (ESI) available: Experimental details, 1H NMR spectra of equilibration experiments, and full characterization of new compounds. See DOI: 10.1039/c0sc00421a

The concept of cyclopropenium activation has been extended to include dehydrative rearrangements in the context of the Beckmann rearrangement. Geminal dichlorocyclopropenes are shown to rapidly and efficiently convert oximes to amides at room temperature, with reactivity that far surpasses other organic-based promoters. Twelve total examples are provided, including a complex steroidal substrate on preparative scale. Evidence is provided that suggests previously reported organocatalytic Beckmann rearrangements may in fact be self-propagating rather than catalytic. The concept of cyclopropenium activation has been extended to include dehydrative rearrangements in the context of Beckmann rearrangements.